Maltitol is one of sugar alcohols and is a useful substance widely used in the fields of foods, drugs, cosmetics, and so on.
The existence of powder products of maltitol has been known since around 1974 (see e.g., Patent Document 1). However, maltitol powders known at that time were free from crystals and became sticky immediately on exposure to air by absorbing moistures due to their exceedingly strong hygroscopicity. Therefore, they could not serve as commodities that endure delivery or storage.
The existence of crystals among various sugar alcohols has been known since a long time ago for sorbitol, mannitol, and the like. However, the crystals of maltitol have been found as recently as 1981.
Practicable maltitol powder products have been put into circulation since 1981 after their crystal products having low hygroscopicity were found. The physical properties thereof and a method for production thereof have been introduced as anhydrous maltitol crystals (see e.g., Patent Document 2).
As described above, practical crystalline maltitol powders have a shorter history of being put into circulation compared to other sugar alcohols. However, they are currently used in wider fields than those for other sugar alcohols, including chewing gum, chocolate, baked goods (e.g., cookies), and other foods or drinks, because their quality and intensity of sweetness are exceedingly similar sugar.
Powder products of sugar alcohols are generally packaged, stored, and delivered in a resin (e.g., polyethylene) inner bag combined with a kraft bag or in a resin inner bag combined with a corrugated cardboard carton. Currently commercially available crystalline maltitol powders adopt also the former or latter packaging form.
However, most of sugar alcohol powder products are highly hygroscopic as compared with other powder products and tend to cause so-called consolidation, in which powder particles form a cluster.
In general, consolidation seen in powdery products means in a broad sense that individual powder particles adhere to each other for some reason such as natural phenomena or artificial manipulation and thereby form a cluster.
In this case, the phenomena include moisture absorption and air drying, and the manipulation includes addition of water, forced drying, compression, and sintering. In a narrow sense, consolidation refers, in many cases, to a formation of cluster via moistures caused by repetitive moisture absorption and drying, after adherence stage between powder particles by liquid film bridging or the like resulting form adsorption of water molecules thereto.
Crystalline maltitol powder products are rated as having low hygroscopicity as compared with other sugar alcohol powder products. Nevertheless, it is known that crystalline maltitol powder products generate consolidation during delivery or storage, as they have hygroscopicity similarly with other sugar alcohol powder products.
The consolidation state of the crystalline maltitol powder products seems to be variously influenced by storage conditions and so on of the products. The consolidation level thereof also varies from a low level of consolidation in which a cluster is easily reduced into powders with a light touch of hand and recovers powder flowability to a high level of consolidation in which a cluster is not reduced even by a strong impact.
In the present specification, consolidation level refers to consolidation of powder particles, specifically, to the presence or absence of consolidated matter and to the strength of the consolidated matter.
Crystalline maltitol powders consolidated during storage or delivery already lose the feature of powder. Such powders not only exceedingly hinder handling in works such as transfer, package opening, pulverization, and dissolution but arise problems including reducing work efficiency, failure of automated equipment and thus difficult to use in a variety of applications. Therefore, their commercial values are drastically reduced.
Various attempts have been made so far in order to solve objects including high hygroscopicity and ease of consolidation presented by sugar alcohol powder products.
These attempts include, for example, (1) a method wherein other components such as silicon dioxide, calcium aluminosilicate, and a surfactant are added and mixed into a sugar alcohol powder in order to prevent consolidation, and (2) a method wherein a desiccating agent such as silica gel is put into a small bag, which is in turn placed between a outer packaging material and an inner bag or in the interior of the inner bag, or a hygroscopic material is confined between a outer material and inner material of an outer packaging material designed to take a double structure.
However, when the former method (1) is applied, the resulting powder presents a problem of cloudiness when dissolved in water. Moreover, there were problems including; impurities mixed into a product largely impair the commercial value thereof; quality of taste, which is an important factor for crystalline maltitol powder products, is changed; and use of a product is limited as additives cannot be used in some fields. Therefore, crystalline maltitol powders obtained by applying this method are absent in the market.
Alternatively, the method (2) was applied in some cases such as crystalline xylitol powder products. However, there were problems including: a desiccating agent might be mixed accidentally into a product in large-scale production; and cost is increased because the method requires adding a hygroscopic material and carefully taking it out in use of the product. Therefore, the adoption of the method is confined to a small number of crystalline xylitol powder products. The method was not adopted for crystalline maltitol powders and is not distributed.
Furthermore, (3) a method for preventing consolidation of powdery sorbitol, characterized by mixing powdery sorbitol in a mixer at a temperature from 50° C. up to melting temperature for 10 or more minutes has been proposed as an attempt to solve the conventional objects (see e.g., Patent Document 3). However, this method requires an operation of mechanically mixing the powder and therefore requires new equipment in addition to conventional production equipment. Moreover, it presents problems such as crush of powder particles cannot be avoided.
Moreover, the above-mentioned method is intended to prevent a phenomenon specific to sorbitol in which “hair-like crystals chronologically develop in a vertical direction from surfaces of sorbitol powder particles and mutually intertwine”. The phenomenon in which hair-like crystals chronologically develop in a vertical direction from surfaces of powder particles has not been observed for crystalline maltitol powders. There have been no cases in which the method was adopted for crystalline maltitol powders based on the premise that such an event would occur.    Patent Document 1: Japanese Laid-Open Patent Application No. 51-113813    Patent Document 2: Japanese Patent Publication No. 63-2439    Patent Document 3: Japanese Laid-Open Patent Application No. 56-133229